INDUCTION MOTORS 



135 



and a curve plotted, giving amperes and pointer position. 

 The motor is then blocked in the position which gives 

 an average value of the current. Form K induction 

 motors are blocked in any position. 



The current is then increased until 150 per cent nor- 

 mal current is obtained, and the amperes, volts and watts 



Fig. 39. Excitation Curve on a 100 H.P., 2080 Volt, 1200 R.P.M., 

 60 Cycle, 3-Phase Induction Motor 



are read. The sign of the wattmeter must be determined 

 in the same way as at the beginning of the excitation 

 test. About six or eight readings should be taken 

 between zero and 150 per cent normal current, but the 

 current should not be held on the motor longer than 

 necessary to secure a reading. After each reading the 

 exciter field should be opened, until ready for the next 

 reading, otherwise the motor will get too hot. As soon 



